Molecular biology of retinoblastoma

Erlotinib has tumor inhibitory effect in human retinoblastoma cells

AIM

In this study, we explored the effect of erlotinib on the development of retinoblastoma (RB) cells both in vitro and in vivo.

METHOD

RB cell lines, Y79 and WERI cells were treated with various concentrations of erlotinib in vitro to assess their cytotoxic profiles. In vitro proliferation, cell-cycle transition and migration were compared between RB cells treated with erlotinib and cells without erlotinib treatment. In in vivo tumorigenicity assay, mice were injected with Y79 cells and orally fed with erlotinib for 28days. The effect of erlotinib on in vivo tumor grafts was then assessed. Western blot analysis on EGFR, ERK, AKT proteins and their phosphorylated proteins was also performed to assess molecular signaling pathways of associated with erlotinib in RB cells.

RESULTS

In vitro erlotinib treatment induced cytotoxicity in Y79 and WERI cells in dose-dependent manner. While Y79 and WERI cells were treated with erlotinib close to EC₅₀ concentrations for 3days, RB proliferation, cell-cycle transition and migration were all significantly inhibited. In in vivo tumorigenicity assay, oral induction of erlotinib also dramatically reduced the growth of Y79 tumor grafts. Western blot demonstrated that, in in vitro RB cells, erlotinib did not alter the protein expression levels of EGFR, ERK or AKT, but significantly reduced the expressions of phosphorylated EGFR, ERK and AKT proteins.

CONCLUSION

Erlotinib was shown to have tumor suppressive effect on RB growth in vitro and in vivo, possibly through the inhibition on EGFR, ERG/AKT signaling pathways.

Expression of NDRG2 in human lung cancer and its correlation with prognosis

We had reported that N-myc downstream–regulated gene (NDRG2) regulates colorectal cancer, breast cancer, clear cell renal cell carcinoma, pancreatic cancer, thyroid cancer and esophageal squamous cell proliferation, development, and apoptosis. The goal of this study was to determine the expression pattern of NDRG2 in human lung cancer and its correlation with prognosis. Immunohistochemistry, RT-PCR and western blot were used to explore the expression of NDRG2 in 185 human lung cancer patients. The correlation of NDRG2 expression with patients’ survival rate was assessed by Kaplan–Meier and Cox regression. Results showed that the expression level of NDRG2 was decreased in human lung cancer tissues, and NDRG2 was positively correlated with depth of invasion (P = 0.038), vascular invasion (P = 0.036), tumor grade (P = 0.039), and tumor size (P = 0.026). Both RT-PCR and Western blots demonstrated that NDRG2 mRNA and protein levels were lower in lung cancer compared to the adjacent normal tissue from the same individual, and NDRG2 level was negatively correlated with UICC stage. Additionally, survival time of lung cancer patients with high expression of NDRG2 was longer than those with low expression during the 5-year follow-up period (P = 0.001). Meanwhile, COX regression analysis indicated that low expression of NDRG2, ≥pT₃, pM₁, ≥pN₁ and vascular invasion were independent, poor prognostic factors of lung cancer patients. These data showed that NDRG2 may play an important role in human lung cancer tumourigenesis, and NDRG2 might serve as a novel prognostic marker in human lung cancer.

Combination of oncolytic adenovirus and endostatin inhibits human retinoblastoma in an in vivo mouse model

There is a critical need for new paradigms in retinoblastoma (RB) treatment that would more efficiently inhibit tumor growth while sparing the vision of patients. Oncolytic adenoviruses with the ability to selectively replicate and kill tumor cells are a promising strategy for cancer gene therapy. Exploration of a novel targeting strategy for RB utilizing combined oncolytic adenovirus and anti-angiogenesis therapy was applied over the course of the current study with positive results. The oncolytic adenoviruses Ad-E2F1 p-E1A and Ad-TERT p-E1 were constructed. The E1 region was regulated by the E2F-1 promoter or the human telomerase reverse transcriptase (hTERT) promoter, respectively. Effects on both replication and promotion of enhanced green fluorescent protein (EGFP) expression were observed in the replication-defective adenovirus Ad-EGFP in diverse cancer cell lines, HXO-RB44, Y79, Hep3B, NCIH460, MCF-7 and HLF. The cancer cell death induced by these agents was also explored. The in situ RB model demonstrated that mice with tumors treated with the oncolytic adenovirus and replication-defective adenovirus Ad-endostatin exhibited notable cancer cell death. This anticancer effect was further examined by stereo microscope, and the survival rate of experimental mice was determined. Both Ad-E2F1 p-E1A and Ad-TERT p-E1 replicated specifically in cancer cells in vitro and promoted EGFP expression in Ad-EGFP, although Ad-E2F1 p-E1A demonstrated superior EGFP promotion activity than Ad-TERT p-E1. In Hep3B, NCIH460 and MCF-7 cells, the number of Ad-TERT p-E1 copies was observed to exceed of the number of Ad-E2F1 p-E1A copies by a minimum of 10-fold. Furthermore, Ad-TERT p-E1 demonstrated significantly superior oncolytic effects in the RB mouse model, and Ad-endostatin effectively suppressed tumor growth and extended the overall lifespan of subjects; however, the Ad-E2F1 p-E1A was clearly less effective in attaining these goals. Most notably, the antitumor effect and survival rate of subjects in the combined Ad-TERT p-E1 + Ad-endostatin group were higher than those treated with either single Ad-TERT p-E1 (p=0.097, p=0.022, respectively) or Ad-endostatin (p=0.037, p=0.006, respectively). In conclusion, application of transcription factor E2F-1 and human telomerase reverse transcriptase (hTERT) promoters to control E1 offer some guarantee that not only is RB gene therapy effective, but it is also safe. Combination therapy using the oncolytic adenovirus Ad-TERT p-E1 and replication-defective adenovirus Ad-endostatin demonstrates desirable oncolysis in the in situ RB mouse model. Additionally, E1B19K is important in the RB tumor suppression effect of oncolytic adenoviruses.

The APC/C Ubiquitin Ligase: From Cell Biology to Tumorigenesis

The ubiquitin proteasome system (UPS) is required for normal cell proliferation, vertebrate development, and cancer cell transformation. The UPS consists of multiple proteins that work in concert to target a protein for degradation via the 26S proteasome. Chains of an 8.5-kDa protein called ubiquitin are attached to substrates, thus allowing recognition by the 26S proteasome. Enzymes called ubiquitin ligases or E3s mediate specific attachment to substrates. Although there are over 600 different ubiquitin ligases, the Skp1-Cullin-F-box (SCF) complexes and the anaphase promoting complex/cyclosome (APC/C) are the most studied. SCF involvement in cancer has been known for some time while APC/C's cancer role has recently emerged. In this review we will discuss the importance of APC/C to normal cell proliferation and development, underscoring its possible contribution to transformation. We will also examine the hypothesis that modulating a specific interaction of the APC/C may be therapeutically attractive in specific cancer subtypes. Finally, given that the APC/C pathway is relatively new as a cancer target, therapeutic interventions affecting APC/C activity may be beneficial in cancers that are resistant to classical chemotherapy.

Epidemiology and Rb1 gene of retinoblastoma

Retinoblastoma (Rb) is the most common eye cancer in children and it can be inherited. Rb is quite rare and originators from the neural retina with a significant genetic component in etiology, which occurs in approximately 1 in every 20 0000 births. In children with the heritable genetic form of Rb, there is a mutation on chromosome 13, called the retinoblastoma 1 (Rb1) gene. Early diagnosis and intervention is critical to the successful treatment of the Rb. The Rb1 gene is the first cloned tumor suppressor gene. As a negative regulator of the cell cycle, Rb1 gene could maintain a balance between cell growth and development through binding to transcription factors and regulating the expression of genes involved in cell proliferation and differentiation. Thus, it is involved in cell cycle, cell senescence, growth arrest, apoptosis and differentiation. We summarized the recent advances on the epidemiology and Rb1 gene of Rb in this review.

Secondary neoplasms after retinoblastoma treatment: retrospective cohort study of 754 patients in Japan

OBJECTIVE

Little is known about the incidence of secondary neoplasms among survivors of retinoblastoma in Japan. The objective of our study was to analyze the cumulative incidence rate of secondary neoplasms following retinoblastoma and to investigate the risk factors of developing secondary neoplasms.

METHODS

We conducted a retrospective cohort study of 754 retinoblastoma patients who visited the National Cancer Center Hospital in Tokyo between 1964 and 2007. The cumulative incidence rate curves were drawn using the competing risk method and compared with the Gray's test. Using competing risk regression analysis, multivariate analysis estimated the subdistribution hazard ratio of factors related to the development of secondary neoplasms.

RESULTS

The median length of follow-up was 108 months (0-594 months). Twenty-one (2.8%) patients developed 23 secondary neoplasms in total. The cumulative incidence rates of secondary neoplasms after retinoblastoma treatment were 2.4% at 10 years after diagnosis, 4.3% at 20 years, 6.4% at 30 years and 19.1% at 40 years. Ten patients (1.3%) died and 723 (95.9%) were alive without developing secondary neoplasms. The subdistribution hazard ratios of hereditary retinoblastoma and external beam irradiation were 4.85 (95% confidence interval = 0.74-31.85) and 4.76 (95% confidence interval = 0.69-33.09), respectively.

CONCLUSIONS

We demonstrated the cumulative incidence rate of secondary neoplasms following retinoblastoma in Japan. The subdistribution hazards ratios of hereditary retinoblastoma and external beam irradiation were high but not significant because of statistical power. The long-term follow-up of retinoblastoma survivors is warranted to understand secondary neoplasm risk.

Inherited cancer syndromes in children and young adults

Geneticists estimate that 5% to 10% of all cancers diagnosed in the pediatric age range occur in children born with a genetic mutation that directly increases their lifetime risk for neoplasia. However, despite the fact that only a fraction of cancers in children occur as a result of an identified inherited predisposition, characterizing genetic mutations responsible for increased cancer risk in such syndromes has resulted in a profound understanding of relevant molecular pathways involved in carcinogenesis and/or resistance to neoplasia. Importantly, because most cancer predisposition syndromes result in an increased risk of a small number of defined malignancies, personalized prophylactic surveillance and preventive measures can be implemented in affected patients. Lastly, many of the same genetic targets identified from cancer-prone families are mechanistically involved in the majority of sporadic cancers in adults and children, thereby underscoring the clinical relevance of knowledge gained from these defined syndromes and introducing novel therapeutic opportunities to the broader oncologic community. This review highlights the clinical and genetic features of many of the known constitutional genetic syndromes that predispose to malignancy in children and young adults.

Mouse fibroblasts lacking RB1 function form spheres and undergo reprogramming to a cancer stem cell phenotype

Activation of the RB1 pathway triggers the cell-cycle arrest that mediates cell-cell contact inhibition. Accordingly, mutation of all three RB1 family members leads to loss of contact inhibition and outgrowth of fibroblasts into spheres where cell-cell contacts predominate. We present evidence that such outgrowth triggers reprogramming to generate cells with properties of cancer stem cells. Fibroblasts with only a single RB1 mutation remain contact inhibited; however, if this contact inhibition is bypassed by forcing the RB1(-/-) cells to form spheres in suspension, cells with properties of cancer stem cells are also generated. These cells not only form tumors in nude mice but also generate differentiated cells. We propose that contact inhibition imposed by the RB1 pathway performs an unexpected tumor suppressor function by preventing cell outgrowth into structures where cells with properties of cancer stem cells can be generated from differentiated somatic cells in advancing cancers.